This invention relates to processes for the production of pentafluoropropenes, and more particularly, to a catalytic process for the dehydrofluorination of hexafluoropropanes to pentafluoropropenes.
Hydrofluoropropenes are useful as materials for the preparation of fluoroplastics, fluoroelastomers and as monomers in the preparation of fluoropolymers.
European Patent Application EP 726 243 discloses a process for the manufacture of 1,2,3,3,3-pentafluoropropene (HFC-1225ye) by the dehydrofluorination of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea). The dehydrofluorination is done in the vapor phase in the presence of a trivalent chromium oxide or partly fluorinated trivalent chromium oxide catalyst.
U.S. Pat. No. 5,396,000 discloses that HFC-236ea can be dehydrofluorinated to HFC-1225ye in the vapor phase in the presence of a catalyst selected from the group consisting of aluminum fluoride, fluorided alumina, metal supported on aluminum fluoride, metal supported on fluorided alumina, and mixtures thereof.
A process is provided for the manufacture of a pentafluoropropene of the formula CFXxe2x95x90CYCF3 where X is selected from H and F and where Y is F when X is H and Y is H when X is F. The process comprises contacting a hexafluoropropane of the formula CF2XCHYCF3 at a temperature of from about 200xc2x0 C. to 500xc2x0 C. with a catalyst, optionally in the presence of an inert gas. The catalyst is selected form the group consisting of (1) catalysts of (a) at least one compound selected from the oxides, fluorides and oxyfluorides of magnesium, zinc and mixtures of magnesium and zinc, and optionally (b) at least one compound selected from the oxides, fluorides and oxyfluorides of aluminum, provided that the atomic ratio of aluminum to the total of magnesium and zinc in said catalyst is about 1:4, or less (e.g., 1:9), (2) lanthanum fluoride, (3) fluorided lanthanum oxide, (4) activated carbon, and (5) three-dimensional matrix carbonaceous materials.
This invention provides a process for producing cis- and trans-1,2,3,3,3-pentafluoropropene (i.e., CF3CFxe2x95x90CHF or 1225ye) from 1,1,1,2,3,3-hexafluoropropane (i.e., CF3CHFCHF2, or HFC-236ea). A process is also provided for producing 1,1,3,3,3-pentafluoropropene (i.e., CF3CHxe2x95x90CF2 or 1225zc) from 1,1,1,3,3,3-hexafluoropropane (i.e., CF3CH2CF3, or HFC-236fa). HFC-236ea and HFC-236fa can be prepared by known art methods. For example, CF3CH2CF3 can be prepared by contacting a mixture of hydrogen fluoride and 1,1,1,3,3,3-hexachloropropane (i.e., CCl3CH2CCl3) in the vapor phase in the presence of a trivalent chromium catalyst as disclosed in U.S. Pat. No. 5,414,165 and CF3CHFCHF2 can be prepared by hydrogenation of hexafluoropropene (i.e., CF3CFxe2x95x90CF2) in the the presence of a Pd/C catalyst.
In accordance with this invention, CF3CHFCHF2 is dehydrofluorinated to CF3CFxe2x95x90CHF and CF3CH2CF3 is dehydrofluorinated to CF3CHxe2x95x90CF2 over a selected catalyst.
Suitable fluorided lanthanum oxide compositions can be prepared in any manner analogous to those known to the art for the preparation of fluorided alumina. For example, the catalyst composition can be prepared by fluorination of lanthanum oxide.
Suitable catalyst compositions can also be prepared by precipitation of lanthanum as the hydroxide which is thereafter dried and calcined to form an oxide, a technique well known to the art. The resulting oxide can then be pretreated as described herein.
The catalyst composition can be fluorinated to the desired fluorine content by treating with a fluorine-containing compound at elevated temperatures, e.g., at about 200xc2x0 C. to about 450xc2x0 C. The pretreatment with a vaporizable fluorine-containing compound such as HF, SF4, CCl3F, CCl2F2, CHF3, CHCIF2 or CCl2FCCIF2 can be done in any convenient manner including in the reactor which is to be used for carrying out the dehydrofluorination reaction. By vaporizable fluorine-containing compound is meant a fluorine-containing compound which, when passed over the catalyst at the indicated conditions, will fluorinate the catalyst to the desired degree.
A suitable catalyst may be prepared, for example, as follows:
La2O3 is dried until essentially all moisture is removed, e.g., for about 18 hours at about 400xc2x0 C. The dried catalyst is then transferred to the reactor to be used. The temperature is then gradually increased to about 400xc2x0 C. while maintaining a flow of N2 through the reactor to remove any remaining traces of moisture from the catalyst and the reactor. The temperature is then lowered to about 200xc2x0 C. and the vaporizable fluorine-containing compound is passed through the reactor. If necessary, nitrogen or other inert gases can be used as diluents. The N2 or other inert diluents can be gradually reduced until only the vaporizable fluorine-containing compound is being passed through the reactor. At this point the temperature can be increased to about 450xc2x0 C. and held at that temperature to convert the La2O3 to a fluorine content corresponding to at least 80% LaF3 by weight, e.g., for 15 to 300 minutes, depending on the flow of the fluorine containing compound and the catalyst volume.
Another suitable procedure for the catalyst preparation is to add ammonium hydroxide to a solution of La(NO3)3.6H2O. The ammonium hydroxide is added to the nitrate solution to a pH of about 9.0 to 9.5. At the end of the addition, the solution is filtered, the solid obtained is washed with water, and slowly heated to about 400xc2x0 C., where it is calcined. The calcined product is then treated with a suitable vaporizable fluorine-containing compound as described above.
Carbon from any of the following sources are useful for the process of this invention; wood, peat, coal, coconut shells, bones, lignite, petroleum-based residues and sugar. Commercially available carbons which may be used in this invention include those sold under the following trademarks: Barneby and Sutcliffe(trademark), Darco(trademark), Nucharm, Columbia JXN(trademark), Columbia LCK(trademark), Calgon PCB, Calgon BPL(trademark), Westvaco(trademark), Norit(trademark) and Barnaby Cheny NB(trademark). The carbon support can be in the form of powder, granules, or pellets, or the like.
Carbons include acid-washed carbons (e.g., carbons which have been treated with hydrochloric acid or hydrochloric acid followed by hydrofluoric acid). Acid treatment is typically sufficient to provide carbons which contain less than 1000 ppm of ash. Suitable acid treatment of carbons is described in U.S. Pat. No. 5,136,113. The carbons of this invention also include three dimensional matrix porous carbonaceous materials. Examples are those described in U.S. Pat. No. 4,978,649, which is hereby incorporated by reference herein in its entirety. Of note are three dimensional matrix carbonaceous materials which are obtained by introducing gaseous or vaporous carbon-containing compounds (e.g., hydrocarbons) into a mass of granules of a carbonaceous material (e.g., carbon black); decomposing the carbon-containing compounds to deposit carbon on the surface of the granules; and treating the resulting material with an activator gas comprising steam to provide a porous carbonaceous material. A carbon-carbon composite material is thus formed.
Other preferred catalysts include catalysts consisting essentially of magnesium fluoride, and catalysts consisting essentially of magnesium fluoride and at least one compound selected from the oxides, fluorides and oxyfluorides of aluminum.
A suitable catalyst may be prepared, for example, as follows:
Magnesium oxide is dried until essentially all water is removed, e.g., for about 18 hours at about 100xc2x0 C. The dried material is then transferred to the reactor to be used. The temperature is then gradually increased to about 400xc2x0 C. while maintaining a flow of nitrogen through the reactor to remove any remaining traces of moisture from the magnesium oxide and the reactor. The temperature is then lowered to about 200xc2x0 C. and a fluoriding agent such as HF or other vaporizable fluorine containing compounds such as SF4, CCl3F, CCl2F2, CHF3 or CCl2FCCIF2, optionally diluted with an inert gas such as nitrogen is passed through the reactor. The inert gas or nitrogen can be gradually reduced until only HF or other vaporizable fluorine containing compounds is being passed through the reactor. At this point the temperature can be increased to about 450xc2x0 C. and held at that temperature to convert the magnesium oxide to a fluoride content corresponding to at least 40% by weight, e.g., for 15 to 300 minutes, depending on the fluoriding agent flowrate and the catalyst volume. The fluorides are in the form of magnesium fluoride or magnesium oxyfluoride; the remainder of the catalyst is magnesium oxide. It is understood in the art that fluoriding conditions such as time and temperature can be adjusted to provide higher than 40 weight% fluoride-containing material.
Another suitable procedure for the catalyst preparation is to add ammonium hydroxide to a solution of magnesium nitrate and if present zinc nitrate and/or aluminum nitrate. The ammonium hydroxide is added to the nitrate solution to a pH of about 9.0 to 9.5. At the end of the addition, the solution is 20 filtered, the solid obtained is washed with water, dried and slowly heated to 500xc2x0 C., where it is calcined. The calcined product is then treated with a suitable fluorine-containing compound as described above.
Yet another procedure for the preparation of metal (i.e., magnesium optionally containing also zinc and/or aluminum) fluoride catalysts containing one or more metal fluorides is to treat an aqueous solution of the metal(s) halide(s) or nitrate(s) in deionized water was treated with 48% aqueous HF with stirring. Stirring is continued overnight and the slurry evaporated to dryness on a steam bath. The dried solid is then calcined in air at 400xc2x0 C. for about four hours, cooled to room temperature, crushed and sieved to provide material for use in catalyst evaluations.
The physical shape of the catalyst is not critical and may, for example, include pellets, powders or granules.
The catalytic dehydrofluorination of CF3CH2CF3 and CF3CHFCHF2 is suitably conducted at a temperature in the range of from about 200xc2x0 C. to about 500xc2x0 C. and preferably from about 375xc2x0 C. to about 450xc2x0 C. The contact time is typically from about 1 to about 450 seconds, preferably from about 10 to about 120 seconds.
The reaction pressure can be subatmospheric, atmospheric or superatmospheric. Generally, near atmospheric pressures are preferred. However, the dehydrofluorination of CF3CH2CF3 can be beneficially run under reduced pressure (i.e., pressures less than one atmosphere).
The reaction can be done in the presence of inert gases such as nitrogen and argon. It has been found that inert gases can be used to increase the dehydrofluorination (DHF) of CF3CH2CF3 to CF3CHxe2x95x90CF2. Of note are processes where the mole ratio of inert gas to CF3CH2CF3 fed to the dehydrofluorination is from about 5:1 to 1:1. Nitrogen is a preferred inert gas. Inert gases have essentially no effect on the DHF of CF3CHFCHF2 to CF3CFxe2x95x90CHF.
Unreacted starting material can be recycled to the reactor for the production of additional CF3CFxe2x95x90CHF (1225ye) and CF3CHxe2x95x90CF2 (1225zc). The hydrofluoropropenes 1225ye and 1225zc may be recovered from the reaction product and any unreacted hydrofluoropropanes by conventional procedures such as distillation.
The process of this invention can be carried out readily in the vapor phase using well known chemical engineering practice.